Conventional hydraulically driven pump-injectors with actuating mechanism comprise: a body with inlet and outlet channels for the connection with accumulator (rail) of actuating fluid (which is in turn connected to the actuating fluid pump), and a drain tank or sump, respectively; pressure intensifier, comprising a power piston and a pumping plunger, a working cavity being formed above the said power piston in the body, into which the actuating fluid is introduced via said inlet channel in the body, and a drain cavity under the power piston connected to the drain tank or sump by an additional channel being formed in the said body; distributing device with a valve, predominantly having an electromagnetic drive controlled by an electronic control unit mounted in the body between said inlet and outlet channels, and the working cavity above the power piston; a return mechanism of the power piston with pumping plunger, and a sprayer unit.
When high factors of pressure multiplication (10 and more) are used, which are needed for obtaining high injection pressure (2000 bars and above) with moderate pressure of the actuating liquid (up to 200 bars), the power piston in conventional pump-injectors with single-piston pressure intensifier must necessarily have a large diameter. As a result, the pump-injector body also has a large diameter. This makes it difficult to modify and upgrade existing diesel engines to incorporate advanced fuel injection systems based on hydraulically driven pump-injectors, due to space limitations in the engines cylinder head, where relatively small diameter injectors or pump-injectors are used.